In conventional power transmission belts, the belt has an inner compression section, an outer tension section, and an intermediate neutral plane. Typically, helically wound reinforcing cords are located within the neutral plane and so the neutral plane is also referred to as the load carrying zone. Such belts also having a variety of groove and rib configurations, using longitudinal or transverse grooves or a combination of both. The grooves are located in the inner compression section of the belt. The grooves assist in engaging a pulley in the power transmission system. For some belts, grooves and rib configurations may also be provided in the outer tension section.
The reinforcing cords in the load carrying zone provide a majority of the tensile strength to the belt. Thus, the materials forming the belt are important. It is known to use high modulus material for the reinforcing cords, including the use of poly(p-phenylene-2,6-benzobisoxazole). However, due to the distinct physical properties of the PBO yarns, simple substitution of PBO yarns for known polyester or aramid cords in power transmission belts may not yield a belt having acceptable performance properties.